Tiny LED indicator lamps have been widely used in electronics, toys, decorations and displays. These standard or conventional LEDs based on AlInGaN or AlInGaP have a typical chip area (or die size) of approximately 0.3 mm by 0.3 mm. These LED lamps typically operate with a DC current of 20 milliamps and a corresponding DC voltage between 2 volts and 4 volts, depending on the LED semiconductor materials. The standard indicator lamp with a T1 or T1-¾ package may have a maximum input power of about 0.1 watt.
Although the intrinsic low voltage and DC current nature of the standard LED lamp makes it very convenient to be incorporated in electronics design, it may also be an inconvenience in other applications. For example, in order to use these standard indicator lamps for Christmas tree decorations, the LED-based light strings must employ parallel wiring of individual LEDs, a bulky step-down transformer and rectifier conversion scheme. LED light strings may also employ serial wiring of individual LED lamps with the number of LED lamps dependant on the AC supply voltage. In the serially connected string, the number of LED lamps cannot easily be changed, and further, if one lamp fails and leads to an open circuit, the entire string will not work.
A standard-size LED array may be integrated on the same substrate with a total device size from around 1 mm by 1 mm to 2 mm by 2 mm or even larger for 120 VAC supply. The device runs under a current of approximately 20 mA or higher to achieve a high brightness for applications such as household lighting purpose. Such an AC-LED needs special packaging and heat dissipation scheme because of the relatively large chip size and high thermal production, which is not compatible with packaging requirements of low power indicator lamps. These power AC-LEDs are not suitable to replace the standard tiny LED indicator lamps.
In U.S. Pat. No. 6,410,940, a micro-size LED (micro-LED) array is disclosed, which is arranged in matrix format to be individually addressed for applications such as a micro-size display, or the array may be arranged in a parallel format to enhance the light output compared with the standard broad area LED. Basically, these micro-LED arrays still work under a low DC voltage (several volts) with a typical current level of tens of mA.
An individual micro-LED has a typical size of hundreds times smaller than the standard LED, and its area is even smaller than the contacts area of the standard LED, therefore, the device geometry layout design and fabrication process are considerably different from each other. The micro-LED array for high voltage AC/DC application is also different from that of the standard-size LED array. A need remains for a micro-size light emitting diode array, which may be powered by standard high voltage AC/DC power and may be used to replace the conventional low DC voltage indicator lamps.